Bicycles are subjected to significant vibration when the rear wheels engage bumps, depressions, or other uneven road or terrain conditions, which can result in rider discomfort, reduced speed, or even safety concerns. While systems are known for providing coil spring shock absorbers, or the like, for the rear portions of bicycle frames, these structures are expensive, and add a significant amount of weight to the bicycle, both of which are undesirable. Therefore it is desirable to be able to provide effective absorption of high frequency, low amplitude vibration in a relatively inexpensive manner that does not add a significant amount of weight to a bicycle frame.
According to the present invention a bicycle frame is provided which can absorb high frequency, low amplitude vibration and uses an existing frame member (namely the seat stays) as a spring for that purpose. Effective damping is also provided for the spring, and the structures providing the spring and damping results are lightweight and relatively inexpensive. Also the components according to the invention allow for ready adjustment of the spring constant and damping effect to accommodate different rider weight, riding style, road or terrain conditions, and other factors.
According to one aspect of the present invention a bicycle frame is provided comprising, as is conventional, a downtube, a seat tube, a cross bar, a fork, a head tube, a pair of chain stays, a rear drop-out, and a pair of seat stays, the chain stays operatively connected to the drop-out and to the seat tube, the cross bar operatively connected between the seat tube and the head tube, the downtube operatively connected between the seat tube and the head tube, and the fork operatively connected to the head tube. The seat stays, which are unique according to the invention, have a first end operatively connected to the seat tube, and a second end operatively connected to the rear drop out (as is conventional per se), with each of the seat stays also each comprising an arcuate portion thereof closer to the second end than the first end, and convex with respect to the chain stays. The seat stays are curved, positioned, and dimensioned so as to act as a spring if the drop out of the frame is subjected to bump forces (which it will be during normal operation).
Each of the seat stays may have a substantially circular arcuate portion subtending an angle of about 20-60 degrees, preferably about 40-50 degrees (e.g. about 45 degrees), and having a radius of between about 11-16 inches (preferably about 12-14 inches, e.g. a little more than 13 inches). The second end of each of the seat stays is preferably pivotally connected (in any conventional manner, such as with a pivot pin) to the rear drop out for pivotal movement about an axis substantially transverse to the dimension of elongation of the chain stays (that is parallel to the axis of rotation of the rear wheel).
The bicycle frame according to the invention further comprises means for substantially simultaneously increasing the spring constant of at least one of the seat stays (preferably both) while damping spring action thereof, when the rear drop out is subjected to bump forces. The simultaneous means may comprise a shock absorber mounted between the seat stays and other frame components, such as the seat tube, chain stays, or the like, with the shock absorber having any conventional configuration. However preferably the simultaneous means comprises an elastomeric material connected between the seat stay at the convex arcuate portion thereof, and a non-elastomeric material (but preferably flexible) support, such as a strip of metal (such as steel, preferably stainless steel). The strip of metal may be bolted to the seat stay for secure attachment but ready removal, the bolts passing through openings in the metal support and the elastomeric material. When the metal support is readily releasably connected to the seat stay, another simultaneous means, with a different effective damping and spring constant, may be readily substituted therefor in order to achieve the adjustability objectives of the invention.
The elastomeric material preferably comprises silicone, and preferably has a durometer between about 20-70 Shore A. Also the elastomeric material preferably has an arcuate surface which engages the seat stay and corresponds to the generally circular configuration of the seat stay. The seat stay may be tapered, and the elastomeric material surface that engages the seat stay will then have a taper and configuration corresponding to that of the seat stay. Threaded inserts may be provided within the seat stay for receipt of the bolts for connecting the simultaneous means to the seat stay.
Preferably the elastomeric material is bonded to the metal strip support, and different such damping and spring force constant-increasing elements may be provided for ready substitution to adjust spring constant and damping effect. When the rider hits a bump, the bump force pushes up on the rear wheel, causing the seat stay to flex and tighten its curve. As the curve tightens it compresses the elastomeric material (silicone) between the seat stay and the metal support. The elastomeric material resists compression and increases the spring rate of the seat stay while simultaneously providing damping to the entire spring system.
According to another aspect of the present invention a bicycle frame is provided comprising as conventional components: a downtube, a seat tube, a cross bar, a fork, a head tube, a pair of chain stays, a rear drop-out, and a pair of seat stays, the chain stays operatively connected to the drop-out and to the seat tube, the cross bar operatively connected between the seat tube and the head tube, the downtube operatively connected between the seat tube and the head tube, and the fork operatively connected to the head tube. The seat stays each have a first end operatively connected to the seat tube, and a second end operatively pivotally connected to the rear drop out for pivotal movement about an axis substantially perpendicular to the dimension of elongation of the chain stays (substantially parallel to the rear wheel axis of rotation), and the frame further comprises a combination damping and spring force-providing element mounted to each of the seat stays for providing a spring force resisting pivotal movement of the seat stays, and providing damping thereof.
The combination element preferably comprises an elastomeric material (such as silicone having a durometer between about 20-70 Shore A) connected between the seat stay at a portion thereof facing the chain stay, and a non-elastic material support (such as a strip of metal, such as stainless steel). Preferably the non-elastomeric material support is releasably connected to the seat stay so that another combination element with a different effective damping and spring constant may be readily substituted therefor.
The invention also relates to a vibration damping and spring force-providing set of a plurality of elements for use with a bicycle frame, per se. Each of the elements comprises an elastomeric material portion having a concavely curved first surface, and a substantially planar second surface, opposite the first surface, and a plurality of through extending openings passing through the first and second surfaces for receiving fasteners therein; and a flexible metal strip contacting the second surface and having openings aligned with the openings in the elastomeric material portion. Each of the elastomeric material portions preferably have a durometer between about 20-70 Shore A, and each elastomeric material portion has a durometer at least about 5 (e.g. at least about 10) Shore A units different than the other elastomeric portions of the other elements of the set. Preferably the elastomeric material portions are bonded to the metal strip, but if desired the elastomeric material components may be separate and the same metal strip may be used to hold different durometer elements in place. For example a set may comprise one element having a 25 Shore A durometer elastomeric material portion, with others having durometers of 40, 55, and 65.
It is the primary object of the present invention to provide a bicycle frame and associated components for effectively, yet in a relatively inexpensive manner and without adding a large amount of weight to the bicycle frame, absorb high frequency and low amplitude vibration during normal use of the frame. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.